Tilt detector and system

ABSTRACT

A tilt detector is provided especially for use in operating subsea drilling equipment including a tool stack at the ocean floor. One such detector is carried by the stack to produce a first output; another detector is carried by a riser pipe near a ball joint interconnecting the stack and pipe to produce a second output, and the outputs are processed to facilitate maneuvering of a drilling vessel. The detector includes: A. A CONTAINER, B. LIQUID IN THE CONTAINER HAVING AN UPPER SURFACE TENDING TO REMAIN GENERALLY HORIZONTAL AS THE CONTAINER TILTS, AND C. SENSORS HAVING INDEPENDENTLY MOVABLE MEMBERS ENGAGING THE LIQUID AT SPACED LOCATIONS TO SENSE THE RELATIVE LEVELS OF THE LIQUID SURFACE AT SAID LOCATIONS AND RELATIVE TO THE CONTAINER DURING SAID TILTING.

United States Patent [191 Crask [451 Oct. 14, 1975 TILT DETECTOR ANDSYSTEM [75] Inventor: Geoffrey J. Crask, Santa Ana, Calif.

[73] Assignee: Hydril Company, Los Angeles,

Calif.

22 Filed: Feb. 25, 1974 21 Appl. No.: 445,639

[52] US. Cl. 33/378 ;33/l H; 33/366 [51] Int. Cl. G01C 9/22; GOlC 9/06[58] Field of Search 33/365, 366, 367, 377, 33/378, 1 H

[56] References Cited UNITED STATES PATENTS 738,407 9/1903 Cable 33/3781,423,529 7/1922 King et a1. 33/378 1,552,691 9/1925 Girvin 33/3781,576,470 3/1926 Richardson.... 33/378 2,804,692 9/1957 Karstens 33/366FOREIGN PATENTS OR APPLICATIONS 678,826 12/1964 ltaly.... 33/367 301,0989/1932 Italy 33/377 213,790 2/1961 Austria 33/378 630,173 4/1936 Germany33/366 Primary Exa'minerHarry N. Haroian Assistant Examiner-Richard R.Stearns Attorney, Agent, or FirmWilliam W. Haefliger [57] ABSTRACT Atilt detector is provided especially for use in operating sub-seadrilling equipment including a tool stack at the ocean floor. One suchdetector is carried by the stack to produce a first output; anotherdetector is carried by a riser pipe near a ball joint interconnectingthe stack and pipe to produce a second output, and the outputs areprocessed to facilitate maneuvering of a drilling vessel. The detectorincludes:

a. a container,

b. liquid in the container having an upper surface tending to remaingenerally horizontal as the container tilts, and

c. sensors having independently movable members engaging the liquid atspaced locations to sense the relative levels of the liquid surface atsaid locations and relative to the container during said tilting.

8 Claims, 24 Drawing Figures US. Patent Oct. 14, 1975 Sheet 2 of73,911,592

US. Patent Oct. 14, 1975 Sheet 3 of7 US. Patent Oct. 14, 1975 Sheet 5 0f7 U.S. Patent Oct. 14, 1975 l IG 9c.

Sheet 6 of7 3,911,592

U.S. Patent Oct. 14, 1975 Sheet 7 of7 3,911,592

TILT DETECTOR AND SYSTEM BACKGROUND OF THE INVENTION This inventionrelates generally to tilt detection, and more particularly concerns theprovision of a tilt detector of improved construction and its use in asystem for aligning a sub-sea riser pipe with a stack of sub-sea wellhead equipment.

There is a continuing need for tilt detection equipment characterized bysimplicity, rugged construction, insensitivity or low sensitivity tovibration (enabling use on well drilling equipment), two axis tiltsensitivity, immunity to temperature drift, and capability for operationafter inversion despite use of liquid mercury as a pendulum. There isalso need for a simple control system for maintaining alignment of ariser pipe with subsea well head equipment. No prior equipment meets theabove needs in the unusually advantageous manner as will be describedherein.

SUMMARY OF THE INVENTION Basically, the tilt detector of the inventioncomprises a container; liquid (as for example mercury) in the containerhaving an upper surface tending to remain generally horizontal as thecontainer tilts, and sensors having independently movable members (asfor example floats engaging the liquid at spaced locations to sense therelative levels of the liquid surface at spaced locations and relativeto the container during such tilting. As will be seen, the liquid in thecontainer may define pools having restricted intercommunication, thepools respectively engaged by the sensors, thereby to provide reducedsensitivity to vibration; the floats may have upper surfaces which taperupwardly to drain liquid off the floats and into the pools; and thesensors may include plungers carried by the floats (the plungerscarrying cores magnetically coupled to differential transformer coils),the plungers having cross sections to form liquid drainage spaces, forreturn' flow to the pools.

' It is another object of the invention to provide first and secondpools as described, to float first and second floats at opposite sidesof an upright axis defined by the detector, and third and fourth poolsto float third and fourth floats at opposite sides of that axis, thefirst and second floats and associated plungers located in 90 relationto the third and fourth plungers and associatedv plungers, thereby toprovide enhanced sensitivity to tilt in two planes, as well astemperature change insensitivity, as will be described.

It is a still further object of the invention to provide two detectorsas described, one adjustably carried by a sub-sea stack of well headequipment, and the other adjustably carried by a riser pipe above a balljoint. As will be seen, control means is provided at the ocean surface,as for example on a drilling vessel, and is oper- DRAWING DESCRIPTIONFIG. 1 is a schematic diagram of a sub-sea riser tilt control system;

FIG. la is a-more complete schematic of the FIG. 1 system;

FIG. 2 is an elevation, in section, showing details of construction ofone preferred transducer, as used in FIGS. 1 and 1a;

FIG. 3 is a view like FIG. 2, showing a tilted condition of the FIG. 2transducer;

FIG. 4 is a section taken on line 44 of FIG. 2;

FIG. 5 is an enlarged elevation, partly in section showing theconstruction of a float as used in the transducer;

FIG. 6 is an end view of the FIG. 5 float;

FIG. 7a is an elevation showing one alignment condition of a sub-seariser and stack;

FIG. 7b is a top plan view of the drilling vessel shown in FIG. 7a;

FIG. 7c is a view of a surface display panel associated with the FIG. 7acondition;

FIG. 8a is an elevation showing another relative alignment condition ofthe sub-sea riser and stack first shown in FIG. 7a, and as related tothe drilling vessel;

FIG. 8b is a top plan view of the drilling vessel shown in FIG. 8a;

FIG. is a view of the surface display panel indicating stack tilt forFIGS. 8a and 811;

FIG. 8d is'a view of the surface display panel indicating lower risertilt for FIGS. 8a and 8b;

FIG. 82 is a view of the surface display panel indicating ball jointerror for FIGS. 8a and 8b;

FIG. 9a is an elevation showing a further relative alignment conditionof the sub-sea riser and stack, as related to the drilling vessel;

FIG. 9b is a top plan view of the drilling vessel shown in FIG. 8a;

FIG. is a view of the surface display panel indicating ball joint errorfor FIGS. 9a and 9b;

FIG. 10a is an elevation showing a still further relative alignmentcondition as between the sub-sea riser and stack and the :drillingvessel, the relative heading of which has changed from FIG. 9a and 9b;

FIG. 10b is a top plan view of the drilling vessel shown in FIG. 10a;

FIG. is a view of the surface display panel indicating ball joint errorfor FIGS. 10a and 10b;

FIG. 1 l is a view of differential transformer circuitry; and

FIGS. 12-13 are circuit diagrams.

DETAILED DESCRIPTION Referring first to. FIG. 1, two tilt detectors ortransducers l0 and 11 are shown in combination with subsea well headequipment 12. One detector 10 is carried by the equipment stack 12a, andthe other detector 1 1 is carried by a riser pipe 13 projectinggenerally upwardly from the stack. A ball joint 12b connects the lowerend of the riser pipe 13 with stub casing 14 associated with the stack,allowing the riser to pivot angularly about that joint, as influenced bychanges in surface vessel position and/or by underwater currents,without deflecting or displacing the stack. The riser normallyprotectively contains pipe or tubing extending between the surface andthe stack at the ocean floor. Merely as illustrative, the stack may alsoinclude a well blow-out preventer 16, well head connectors 17 and 18, amud valve 19, and other equipment. Also shown are guy wires and guides21 therefor attached to the stack via bracket arms 22, enabling guidedlifted and lowering of the stack between the surface and the ocean floor23. FIGS. 7a, 7b; 8a and 8b; 9a and 9b; and 10a and 10b also showvarious relative orientations of a surface vessel, sub-surface stack,and riser pipe extending therebetween, as will be described.

FIG. la illustrates, schematically, the detector or transducer 10carried by the stack 12 as via a mounting and leveling plate 24. Thedetector may be connected with plate 24 as via a universal pivotconnection 25 and three leveling screws 26 having threaded connectionwith plate 24 may be adjusted as respects their bearing against theunderside of the detector to initially align the detector axis 10a inparallel relation with the stack vertical central axis schematicallyindicated at 27. Similarly, the detector or transducer 11 is carried bythe riser pipe 13 as via a mounting or leveling plate 28. Detector 11may be connected with plate 28 as by universal pivot connection 29, andthree leveling screws having threaded connection with plate 28 may beadjusted as respects their bearing against the underside of detector 11to initially align the detector axis 11a in parallel relation with theaxis 28a of the lower end of the riser. Accordingly, means is providedto adjust the angularities of the detectors relative to the stack and tothe riser pipe, respectively.

FIG. Ia also shows, schematically, an armored signal cable 29a extendingbetween a cable reel 30a at the surface and the detectors. As seen, aplug connection 31 at the lower end of the cable may fit a socket at 32associated with transducer or detector 11; and a jumper cable 33 mayhave plug connection at 34 with a socket 35, and plug connection at 36with a socket 37. The latter is associated with transducer 10, and theformer socket 34 has electrical connection with plug 31 via socket 32.Accordingly, the transducer outputs are transmitted to the surface viaseries cables 33 and 29a. The upper reeled end of cable 29a hasconnection with surface display circuitry 38 via a jumper cable 39, thecircuitry 38 having an analog output at 40 to a strip chart recorder 41,an output at 42 to an alarm relay 43, and a digital output at 44 to acomputer 45.

Referring now to FIGS. 2-6, the tilt detector 10 (which is alsorepresentative of detector 11) basically comprises a container; liquidin the container having an upper surface tending to remain generallyhorizontal as the container tilts; and sensors having independentlymovable members engaging the liquid at spaced location to sense therelative levels of the liquid surface at such locations and relative tothe container, during such tilting. In the. example, the container isshown to comprise a receptacle shaped body having a base 134, an annularupper rim 135 defining a bore 136;an inner upwardly facing shoulder 137;and four like recesses or wells 138a-138d sunk downwardly in the bodyfrom the inner surface 137.

The container also includes a cap or casing 139 which fits downwardly at39a into the bore 136 and has a lower end face seating against shoulder137, there being a central fastener 140 which connects the cap to thebody. O-ring seal 142 seals off between the bore 136 and the casing 139,whereby the wells 138a-138d are sealed off from the exterior; however,there are lateral ports 143-146 drilled in the body 133 to restrictivelyintercommunicate the lower interiors of the wells, as shown, wherebyliquid such as mercury in the wells drains from higher to lower wellsduring tilting of the detector. Such ports dampen or slow changes inmercury level in the wells during changes in detector tilt, so that amore accurate output signal (indicative of tilt) is realized, as willappear.

Pools of mercury or other suitable liquid in the wells are indicated at47-50.

The movable sensor members referred to above may with unusual advantagecomprise plastic floats 51-54 having convex undersides, indicated at 55,to effectively engage the liquid mercury pool surface during variousconditions of tilt, as for example as illustrated in FIG. 3; also, thefloats have frusto-conically upwardly tapering upper sides 56, toeffectively shed mercury wetting such upper sides after return of thedetectors to near FIG. 2 upright position following extreme tilt orinversion of the unit. Further, the floats carry plungers 58 movableendwise within bores 70 formed by differential transformer coils 60-62.Magnetic cores 63 carried by the plungers have variable magneticcoupling with the coils, depending on the endwise position of the cores,as is also clear from the FIG. 11 differential transformer circuit. Asthere shown, the output of oscillator 65 is impressed on coil 61 withwhich differentially wound coils 60 and 62 are inductively coupled. TheDC output at 67 of a demodulator 66 connected with coils 60 and 62 is afunction of the endwise position of the core 63. Accordingly, the tiltof the detector determines the core position relative to the coils,which in turn determines DC output of the differential transformerassociated with each core. Two such floats such as at 51 and 52 locatedat 90 angles about the detector axis 10a are sufficient to determine theazimuthal direction of tilt and the degree of such tilt; however, thetwo additonal floats 53-54 and associated circuitry serve to increasethe accuracy of the equipment and also provide temperature driftinsensitivity. Thus, the outputs of transformers associated with 180angle related floats 51 and 53 may be added, i.e. differenced, to obtainan analog DC value representative of tilt in one (port and starboard)direction, whereas the outputs associated with 180 related floats 52 and54 may be added to obtain an analog DC value representative of tilt inanother (fore and aft) direction. Temperature change induced changes inmercury level do not affect the difference output referred to.

From FIGS. 2-6, it will be seen that the plungers have generallypolygonal (as for example generally triangular) cross sections alongplunger lengths movable endwise within guide bores 70 surrounded by thecoils, thereby to form liquid drainage spaces 71 between the bore andplungers. Accordingly, liquid mercury never collects between theplungers and bores to impede endwise travel of the plungers in thebores, when the detector is in upright position, but rather such mercuryfreely drains via the spaces 71 back into the pools 47-50 as described.

Referring now to FIG. 12, it will be seen that the port and starboard"analog output at of the stack transducer 10 may be passed via switch 81and lead 82 to an analog to digital converter 79 and thence at 83 to aport and starboard digital display; and fore and aft analog output at 84of transducer 10 may be passed via switch 85 and lead 86 to the ADC 79and thence at 87 to the fore and aft digital display. Alternatively, the

port and starboard analog output at 88 of the lower riser transducer 11may be passed via switch 89 and lead 90 to ADC 79 and thence to display83; and fore and aft analog output at 91 of transducer 11 may be passedvia switch 92 and lead 93 to the ADC 79 and thence to display 87. Inaddition, a so-called port and starboard ball joint error analog outputat 94 may be obtained by adding at 95 (i.e. differencing) the outputs 80and 88 of the transducers and 1 1, and the output 94 may be passed via aswitch 96 to the ADC 79 for digital display at 83. Similarly, aso-called fore and aft ball joint error analog output at 97 may beobtained by adding at 95 (i.e. differencing) the outputs 84 and 91 ofthe transducers 10 and 1 1, and the output 97 may be passed via a switch99 to ADC 79 for digital display at 87. The FIG. 13 circuit may be usedat 95 in FIG. 12. Finally, an upper riser transducer 201 may be providedwith connections similar to those for the lower riser transducer 11.Heading correction equipment 225 may be connected in series with the ADCat the input side thereof, and its use will be described in terms ofcorrecting the analog input to the ADC.

FIG. 7c shows a panel having a DEGREES TILT DIS- PLAY 101 that includesPORT and STARBOARD 2- digit displays 83a and 83b, and FORWARD and AFT2-digit displays 87a and 87b. In addition, in ZERO TILT display 100 isprovided, and includes a FORE and AFT (F/A) section 101a whichilluminates when FORE and AFT tilt is zero, and a PORT and STAR- BOARDsection 10112 which illuminates when Port and Starboard tilt is zero.

The following examples of Riser/Stack Alignment are provided to give abetter understanding of the various situations in which the system canbe used. In all of the examples, the DEGREES TILT Display 101 indicatesthe position of the transducers with respect to true vertical. The BALLJOINT ERROR indicates the TILT ERROR difference between the lower risertransducer and the stack transducer. The direction in which the drillingvessel 102 needs to move (as seen in FIG. 7b) in order to align theriser with the stack 12 is opposite from that displayed. In other words,if a starboard ball joint error is indicated, the drilling vessel mustmove to the port in order to align the riser 13 with the stack.

Example No. 1 (Refer to FIGS. 7a to 70) In FIG. 7a the stack 12 is shownperfectly vertical and the drilling vessel 102 is directly over thestack. In this perfect condition, there is 0 ball joint error which isindicated by both sections 100a and 100b of the ZERO TILT Display beingilluminated. A display of ball joint error is achieved by depressingswitches or pushbuttons 96 and 99. Note: When there is 0 tilt in a planethe two digital displays associated with that plane will be dark. Theappropriate section of the ZERO TILT Display will be illuminated.

In FIG. 7c the stack heading has been entered on a STACK HEADING SWITCH103 as 330. Since the drilling vessel heading in FIG. 7b is identical tothe stack heading, a HEADING DEVIATION switch 104 is set to 0. Thesignificance of switches 103 and 104 will be discussed later.

Example N0. 2 (Refer to FIGS. 8a, 8b, & 80)

In FIG. 80 the DEGREES TILT Displays are indicating the tilt registeredby the stack transducer. This is accomplished by the operator depressingthe STACK pushbutton which closes switches 81 and in FIG. 12 forexample. In this example the stack has a 9.3 tilt to the port. TheForward/Aft Stack Alignment is perfectly vertical and indicated by theF/A Section a of the ZERO TILT Display being illuminated. The stack andvessel are heading due North and are so indicated by the STACK HEADINGAND HEADING DEVIATION switches 103 and 104.

FIG. 8d indicates the tilt measured by the LOWER RISER transducer. Thisis accomplished by the operator depressing the LOWER RISER pushbuttonwhich closes switches 89 and 92 in FIG. 12. In this example we see thatthe lower riser transducer 11 indicates a 3.1 forward tilt and a 2.4starboard tilt. If the drilling vessel in FIG. 8b were moved to the portand aft and directly over the stack, the LOWER RISER DEGREES TILTDisplay would indicate F/A and P/S equal 0. However, because of the porttilt of the stack, the riser and stack would not yet be correctlyaligned.

In FIG. 8e we see displayed the BALL JOINT ERROR which is the differencebetween the riser and stack angularities relative to vertical. If thedrilling vessel is now moved aft and port until the F/A and P/S ZERODisplays 100a and l00b are illuminated, the vessel will be displaced tothe port of the stack. However because of the port tilt of the stack,the riser and stack would then be in proper alignment.

Example No. 3 (Refer to FIGS. 9a, 9b, 9c and FIGS. 10a, 10b and 100) InFIG. 9a the stack alignment is perfectly vertical. A BALL JOINT ERROR of4.8 starboard and 2.8 aft is indicated because the drilling vessel inFIG. 9b is horizontally displaced and not directly over the stack. Thedrilling vessel is heading due North which is the same heading as thestack. In order to obtain proper riser/- stack alignment, the vesselmust move forward and to the port until it is directly over the stack.

In FIG. 10a the stack and riser angles have not changed; however thedrilling vessel is no longer on the same heading as the stack (dueNorth). The new vessel heading of 330 is entered into the display panelby rotating the HEADING DEVIATION switch 104 until the vessel heading isindicated by the COMPASS HEADING Display 120. Without the HEADING DE-VIATION adjustment, the BALL JOINT ERROR Display in FIG. 100 would beidentical to in FIG. 90, indicating 4.8 starboard tilt and 2.8 aft tilt.With that indication, if the drilling vessel were to move forward tocompensate for the aft tilt of the riser, the vessel would be movingfurther away from the stack. In this regard, the HEADING DEVIATIONswitch 104 automatically compensates the BALL JOINT ERROR Display sothat the vessel will be moved in the proper direction to achieve perfectriser/stack alignment. The BALL JOINT ERROR Display in FIG. 10cindicates that, because of the 330 heading deviation, the vessel needonly move to the port to properly align the riser with the stack.

In FIG. 12, compensation input 225 to the ADC corresponds to the inputprovided by switch 104.

Certain important advantages of the detectors and system are summarizedas follows: the use of a fluid metal pendulum as disclosed to sensevertical eliminates need for mechanical pendulum supports subject todamage under shock loading conditions, it combines low natural frequencywith relatively small size, it provides relatively large viscous dampingin conjunction with the flow ports between the wells, and its operationremains unaffected following accidental inversions, and it affords highsurface tension as well as maximum surface position stiffness tomeasuring float position errors; the use of lightweight, plastic floatsto detect fluid pendulum surface position provides for physicalcharacteristics such as low density, lack of electrical conductivity andabsence of magnetic properties, and the positions of the floats areprimarily controlled by fluid surface tension rather than float buoyancyto eliminate errors due to fluid contact angle variations with the floatsurfaces; the float shapes provide independence of fluid contact surfaceshape from tilt angle, elimination of output non-linearities, and thefloat upper surfaces promote drainage of fluid after angle overloads,eliminating zero-shifts; and the float plunger shapes eliminate pendulumfluid hold-up or retention in the guides, as described.

Further, the use of differential transformers to detect float positionsresults in negligible friction or stiffness force application to thefloats and plungers, and such transformers are relatively immune todamage due to shock and vibration and they embody no moving electricalcomponents so that wear is not a factor; the use of dual differentialtransformers enables cancellation of errors due to differentialexpansions of fluid, case and displacement sensor components; theCartesian format, decimal angle, display readouts provide forunambiguous and immediate display of error quadrants, error-free readoutof Cartesian components of angles referred to ship axes, and use of azero error angle target indicator eliminates display ambiguities at zeropoints. Finally, the provision for manual insertion of ship headingcorrection eliminates need for operator mental calculation to correctfor ship heading changes, and the use of low cost axis transformationsallows adequate compensation of the tilt displays, in the range of 1*:10 of tilt, by azimuth increments.

FIG. 13 shows typical electrical connections for a differential pair oftransducers 248 and 249 in one plane, as for example at the stack, lowerriser, or upper riser. Floats 251 and 253 correspond to floats 51 and 53previously described. Note cross-over connection 254 be tween the coilsof the differentially connected transducers, and the output leads 255and 256.

I claim:

1. A tilt detector, comprising,

a. a container,

b. liquid in the container having an upper surface tending to remaingenerally horizontal as-the container tilts,

c. sensors having independently movable members engaging the liquid atspaced locations to sense the relative levels of the liquid surface atsaid locations and with respect to the container during said tilting,

d. there being wells and ports formed in the con tainer, the portsinterconnecting the wells, the liquid in the container defining pools insaid wells and having restricted intercommunication via said ports, saidmembers comprising floats engaging the liquid pools at the surfacethereof,

e. said sensors also including plungers connected to the floats, therebeing differential transfonner coils magnetically coupled to cores onthe plungers, said plungers dimensioned to be movable endwise withinguide bores surrounded by said coils, portions of the cross sections ofsaid plungers being radially different from the cross sections of saidguide bores to form liquid drainage spaces between the plungers andbores communicating with said wells, said bores formed in an upperportion of the container relative to said wells.

2. The detector of claim 1 wherein the detector defines a longitudinalgenerally upright axis, first and second of said pools and correspondingfirst and second sensors are spaced apart in one lateral directiongenerally normal to said longitudinal axis, and third and fourth of saidpools and corresponding third and fourth sensors are spaced apart inanother lateral direction generally normal to both said longitudinalaxis and said one lateral axis.

3. The detector of claim 1 wherein the detector defines a longitudinallygenerally upright axis, and said floats have upper surfaces which slopedownwardly and toward the float peripheries to drain said liquid intosaid pools.

4. The detector of claim 1 wherein said floats have convex undersides toengage said liquid, and upwardly tapering upper surfaces.

5. The detector of claim 1 including circuitry connected with saidtransformer coils to produce an output corresponding to said tilt of thedetector.

6. The detector of claim 5 wherein at least two of said floats arelocated at approximately a angle about an upright axis defined by thedetector.

7. The detector of claim 5 wherein two of said floats are located atopposite sides of an upright axis defined by the detector.

8. A tilt detector comprising,

a. a container,

b. liquid in the container having an upper surface tending to remaingenerally horizontal as the container tilts,

c. sensors having independently movable members engaging the liquid atspaced locations to sense the relative levels of the liquid surface atsaid locations and with respect to the container during said tilting,

d. there being wells and ports formed in the container, the portsinterconnecting the wells, the liquid in the container defining pools insaid wells and having restricted intercommunication via said ports, saidmembers comprising floats engaging the liquid pools at the surfacethereof,

e. said sensors also including plungers connected to the floats, therebeing differential transformer coils magnetically coupled to cores onthe plungers, said plungers having generally polygonal cross sectionsalong plunger length dimensioned to be movable endwise within generallycircular guide bores surrounded by said coils, thereby to form liquiddrainage spaces between the plungers and bores, said bores formed in anupper portion of the container.

1. A tilt detector, comprising, a. a container, b. liquid in thecontainer having an upper surface tending to remain generally horizontalas the container tilts, c. sensors having independently movable membersengaging the liquid at spaced locations to sense the relative levels ofthe liquid surface at said locations and with respect to the containerduring said tilting, d. there being wells and ports formed in thecontainer, the ports interconnecting the wells, the liquid in thecontainer defining pools in said wells and having restrictedintercommunication via said ports, said members comprising floatsengaging the liquid pools at the surface thereof, e. said sensors alsoincluding plungers connected to the floats, there being differentialtransformer coils magnetically coupled to cores on the plungers, saidplungers dimensioned to be movable endwise within guide bores surroundedby said coils, portions of the cross sections of said plungers beingradially different from the cross sections of said guide bores to formliquid drainage spaces between the plungers and bores communicating withsaid wells, said bores formed in an upper portion of the containerrelative to said wells.
 2. The detector of claim 1 wherein the detectordefines a longitudinal generally upright axis, first and second of saidpools and corresponding first and second sensors are spaced apart in onelateral direction generally normal to said longitudinal axis, and thirdand fourth of said pools and corresponding third and fourth sensors arespaced apart in another lateral direction generally normal to both saidlongitudinal axis and said one lateral axis.
 3. The detector of claim 1wherein the detector defines a longitudinally generally upright axis,and said floats have upper surfaces which slope downwardly and towardthe float peripheries to drain said liquid into said pools.
 4. Thedetector of claim 1 wherein said floats have convex undersides to engagesaid liquid, and upwardly tapering upper surfaces.
 5. The detector ofclaim 1 including circuitry connected with said transformer coils toproduce an output corresponding to said tilt of the detector.
 6. Thedetector of claim 5 wherein at least two of said floats are located atapproximately a 90* angle about an upright axis defined by the detector.7. The detector of claim 5 wherein two of said floats are located atopposite sides of an upright axis defined by the detector.
 8. A tiltdetector comprising, a. a container, b. liquid in the container havingan upper surface tending to remain generally horizontal as the containertilts, c. sensors having independently movable members engaging theliquid at spaced locations to sense the relative levels of the liquidsurface at said locations and with respect to the container during saidtilting, d. there being wells anD ports formed in the container, theports interconnecting the wells, the liquid in the container definingpools in said wells and having restricted intercommunication via saidports, said members comprising floats engaging the liquid pools at thesurface thereof, e. said sensors also including plungers connected tothe floats, there being differential transformer coils magneticallycoupled to cores on the plungers, said plungers having generallypolygonal cross sections along plunger length dimensioned to be movableendwise within generally circular guide bores surrounded by said coils,thereby to form liquid drainage spaces between the plungers and bores,said bores formed in an upper portion of the container.